Among all of the strategic tools that poker players have at their disposal, pot odds are among the most useful and important. As the name implies, pot odds indicate the ratio of the size of the pot at any given time to the cost of making a call. Another way of expressing it is a comparison of the amount of money already in the pot to how much it will cost a player to win it.

Pot odds are quite easy to calculate, but a bit more complicated to use well. Some simple examples can be helpful to begin.

In the game known as Texas Hold’em, mandatory “blinds” initiate the betting. Before any cards are dealt, the pot will already contain three units: one from the small blind and two from the big blind. Following the deal, in order to remain in the game, the first player to the left of the big blind must at least match the big blind by calling two units. At this point, the pot odds are 3:2—in order to win three units, two must be risked.

Assuming the first player calls, there will be five units in the pot when the next player has to take a decision. To stay in the game, this player must also wager at least two units, but at this point the pot odds have changed. They have gone up because the pot is bigger. Now the ratio is 5:2—a risk of two units could win five.

For the sake of example, suppose that all of the other players that follow decide to fold until the decision comes to the small blind. At this point, there are seven units in the pot: the two original blinds (1+2) and the two calls (2+2). The small blind contributed one unit before the deal, so only one unit is needed to call. That makes the pot odds 7:1. From a player’s perspective, the higher the pot odds are, the more advantageous the bet will be. Calling is an easy decision for the small blind to take.

As the hand progresses, the pot odds keep changing for each player, depending on how much is in the pot and how much is required to call and remain in play. When the pot contains 100 units and a call costs ten units, the pot odds are 10:1. If a player raises an amount equal to the pot, for the next player in turn the pot odds will drop to 2:1. It takes a little practice, but calculating pot odds really is just as simple as dividing the pot by the amount needed to call.

On the other hand, using pot odds strategically requires one other vital piece of information—the probability of winning the hand. When five players are seated, before any cards are dealt, each of them has a one in five possibility of catching the winning hand. But as soon as the two hole cards are known, that probability changes, favoring pairs, high cards, and suited cards. And after the flop, when the first three community cards are seen, the odds of winning shift yet again.

In order to know what a player’s chances of winning are, one must count the number of “outs” for the hand. An “out” is any card that would improve the hand and the player’s probability of winning.

For example, when holding four suited cards, there are nine outs that can improve it to a flush. When holding an open-ended sequence of four unsuited cards, there are eight outs that can improve it to a straight. Any pair will have two outs that can improve it to a set (three-of-a-kind), and any set will have only one out that can improve it to four-of-a-kind.

When a player knows the number of outs that can turn his/her hand into a winner, it can be used to create a ratio for comparison to the pot odds. In Texas Hold’em, after the flop, there are five cards known and 47 cards unseen. If the number of outs is 12, for instance, the probability of getting a winner on the next card is 12:47 or roughly 1:3. Assuming the pot odds are 3:1 or higher, calling is a smart wager. By the same token, if a player has only six outs, a ratio of 6:47 or about 1:8, the pots odds must be 8:1 or greater to warrant a call.

A note of caution: In determining the number of outs for comparison to pot odds, count only those cards which will improve the hand and turn it into a winner. For example, holding a four-card flush with an Ace showing on the board post-flop, one must assume that some other player has a hidden Ace, so only those outs that would complete the flush or form a set should be counted, not those which would form a small pair—an improvement, but insufficient to win.